Hopefully the engineers will comment on this, but my opinion is that even if
you can put the PVC through the concrete slab, there is no advantage in
doing so.
Here's how I did it: I have three PVC conduit runs from the house to the
tower: 4" for RF cables, 2.5" for control cables and 1" for AC (it's a
motorized crankup.) The conduit is buried 4 feet deep, which is just below
the frost line here in NH. Any higher and frost heaves can deform and
possibly break the PVC. The PVC is the gray type used for buried electrical
runs. The runs are terminated at both ends with 16" diameter 90-degree
sweeps up to weatherproof utility boxes. The sweeps are *not* the 90-degree
adapters you find in the plumbing supply section at the local hardware
store. Sweeps are designed to gradually transition the PVC from horizontal
to vertical, making it much easier to pull the cables through. Pulling
cables is recommended over trying to build the conduit around the cables.
The utitlity boxes are mounted on the side of the house at one end and on a
panel made of pressure-treated lumber at the tower end. There are two boxes
at each end, one for RF/control, the other for AC. The RF/control boxes at
both ends contain grounding panels with Polyphaser lightning suppressors for
every cable. The AC boxes have surge suppressor circut breakers and MOVs
installed. Holes are drilled in the back of the house-mounted boxes,
allowing the cables to exit the suppressors and enter the house just under
the shack floor. The cables go through PVC-lined holes drilled in the floor
under the operating desk. At the tower end, coax runs exit the RF/control
box through the bottom of the box via Polyphaser bulkhead mounted
suppressors. Control cables exit via waterproof feed-throughs. Both sets of
cables run about five feet to the tower, about three feet off the ground. It
would be better to run them straight down to the ground and over to the
tower through some flexible PVC pipe, and bond the coax shields to the
bottom of the tower, but I didn't do that (the coax on the tower is thus
more exposed to lightning damage, but I'm willing to accept that risk.)
Four pieces of 1/0 stranded wire are clamped to the tower bolts and run
across the top of the slab to ground rods a foot or so from the base. The
ground rods are connected with 1/0 radials to two more ground rods each, for
a total of 12 ground rods. All ground rod connections are Cadwelded.
Back before I erected my tower, I put in a 3'x3'x4' concrete block with a 4"
diameter steel tube embedded in it to permanently support my telescope. I
needed to run power and control cables from the computer in the house to the
telescope (for remote control and digital imaging), so I ran PVC from the
house right into the side of the slab and up to the scope, just as you are
suggesting. It works, but this slab isn't exposed to tower-like forces. The
90-degree turn in the PVC did make it tough to pull cables through, however.
In the end, I concluded that there was little benefit to running PVC through
the concrete. A small utility box mounted next to the scope would have been
better. A short length of PVC could have been used to connect the box to the
scope.
73, Dick WC1M
>
> I am installing my 3.5 ft. square tower base soon and was wondering
> about the "proper" method to run the power and signal PVC tubes to the
> concrete base for my crankup tower
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